1. Field of the Invention
The present invention relates to a cleaning blade and, more particularly, to a cleaning blade attached to a cleaning apparatus of an image forming apparatus such as a dry-type electrophotographic copying machine or electrophotographic printer.
2. Description of the Prior Art
Generally, image formation by an image forming apparatus is obtained by firstly scanning the manuscript with an optical system and exposing a photosensitive drum on which a latent image is formed, and then allowing toner to adhere only to the latent image portion in a developing apparatus. The toner image is transferred to paper which has been fed into the machine and fixed in a fixing apparatus, and then the paper on which the image formation has been completed is ejected from the apparatus. From the toner remaining on the photosensitive drum after completion of the image transfer, the remaining electric charge is removed by a discharger. Then, the remaining toner is removed from the drum by a cleaning blade in a cleaning apparatus, and the photosensitive drum is ready to repeat again the image formation cycle. The toner removed and recovered in the cleaning apparatus is recycled and used again in the developing apparatus.
In the cleaning apparatus of the image forming apparatus as described above, a cleaning blade comprising a rubber elastomer (such as urethane rubber) is widely used now, since it lends itself well to small-sized designs, the assuredness with which cleaning can be effected and the re-usability of the recovered toner.
On the other hand, in accordance with the tendency in recent years of driving image forming apparatus at high speed and to reduce maintenance, various consumptive parts of the apparatus are required to have a longer life and, as a matter of course, many proposals to elongate the life of cleaning blades have been presented.
However, the life of cleaning blades is short compared with that of other parts, because it is necessary to increase the pressure of the blades against the photosensitive drum to improve their cleaning ability. The increased pressure on the blades causes excessive wear. To prevent the wear, the pressure on the blades has to be decreased, and conversely the decreased pressure results in a lessening of the cleaning ability. Thus, it would be the ideal situation to diminish the wear without causing a lessening of the cleaning ability of the blades. On the other hand, it is well known that toner particles serve as a lubricant on the contact surface between the blade and the photosensitive drum which acts naturally to prevent wear. Therefore, the problem can be solved by utilizing the service of this lubricant to its maximum.
At the start of an operation just after exchanging the cleaning blade with a new one, however, adherence of the toner to the surface of the blade edge is still insufficient and the resin powder particles, which have been applied to the new blade to protect its surface, scatter simultaneously with the rotation of the photosensitive drum because of the repulsive force due to frictional electrification and the centrifugal force due to its rotation. Thus, in the interval between when a protecting layer of toner particles or resin powder particles are not present on the blade surface, tear breaking arises on both ends of terminal portions of the blade edge surface, as shown in FIG. 5, on account of the large frictional force. Therefore, it is important that the above-mentioned resin powder particles are caused to adhere to the blade edge surface as long as possible and that the toner particles are caused to adhere to the blade edge surface from the beginning. The biggest reason why the resin powder particles scatter, and the toner particles hardly adhere, is due to the fact that the cleaning blade is frictionally electrified as it is pressed onto the photosensitive drum and repulses these particles.
For the purpose of preventing such electrification of the cleaning blades, there have been proposed Japanese Patent Publications Nos. SHO 44-2034, SHO 56-51347, etc., in which cleaning blades are made electroconductive and grounded.
However, the cleaning blades of the above Japanese Patent Publications Nos. SHO 44-2034, SHO 56-51347, etc., have a defect also in that, when they are used in the so-called Carlson process with a selenium series photosensitive drum, an organic photosensitive drum, an amorphous silicon photosensitive drum, or the like, it follows that the surface of the photosensitive drum is grounded in the cleaning step and the electrification on the photosensitive drum becomes difficult in the next step. Also in a method of applying a definite voltage without grounding, there is the problem that it requires other apparatus, i.e., power source parts increasing the apparatus size and complexity.
The purpose of the present invention is to reduce these inherent defects, as mentioned above, by providing a long-life cleaning blade which is free from the wear of the blade edge surface and, particularly, from the tear breaking on both terminal portions of the edge surface, while improving the cleaning ability, and without requiring any other apparatus, such as power source parts.